i) Field of the Invention
The present invention relates to a photo mask for use in manufacturing a semiconductor integrated circuit, and the like, a photo mask blank as a material of the photo mask, and a method of manufacturing the photo mask blank.
ii) Description of the Related Art
In manufacturing of semiconductors such as a semiconductor element, IC and LSI, a manufacturing process of a photo mask for use in transferring a fine pattern onto a semiconductor wafer usually includes: a film forming step of forming films, such as an opaque film, a semi-transmission film (a translucent film), onto a transparent substrate obtained by precisely polishing synthetic quartz glass by sputtering, and the like; a resist coating step of coating a resist film on the films, such as the opaque film, by a spin coating method; an exposure step (delineating step) of irradiating a resist surface with an electron ray or a laser beam to selectively expose the resist film; a development step of developing the exposed resist film with a predetermined developer to form a resist pattern; an etching step of using the resist pattern as a mask to etch the films such as the opaque film and to obtain a predetermined opaque film pattern, and the like. In this case, the substrate thus obtained by the film forming step is generally called a photo mask blank.
Here, in the forming step of forming the opaque film, usually from a viewpoint of productivity, the film is formed by a usual DC magnetron sputtering method by using a DC magnetron sputtering apparatus and a chromium target. Alternatively, a thin film is formed by a reactive sputtering method executed by introducing at least one of gases such as nitrogen and oxygen.
Chromium or a chromium compound is used as the opaque film in an original sheet of the photo mask, that is, a binary photo mask blank, in which light intensity modulation is used to transfer the pattern. In addition, the sputtering method is mainly utilized as a method for forming the opaque film onto the substrate. However, when the opaque film such as a chromium film is formed by the sputtering method, the opaque film usually has a tensile stress, and the photo mask blank including the transparent substrate as a base therefore warps. Such warps bring about a high possibility of an insufficient focus depth for exposure or a design defect. This results in deterioration of the photo mask blank. Here, for a warp amount of the substrate, the substrate is measured by flatness measuring instrument by an optical interferometer, such as FM200 manufactured by TROPEL Co. In this case, a difference of height (P-V value) between a highest point and a lowest point from a level surface of the substrate is measured before and after the film formation, and the warp amount of the substrate generated by the film formation is defined by the difference of the P-V value before and after the film formation. That is, definition is made by:
(warp amount of substrate after film formation)xe2x88x92(warp amount of substrate before film formation)=(warp amount of substrate generated by film formation).
As a stress reduction method of the opaque film, there is a method of applying a bias on a substrate side during sputtering deposition and implanting an ion present in plasma. However, since the photo mask blank has a relatively large film formation area, and the substrate is a dielectric such as glass, it is difficult to obtain a uniform effect in the surface.
On the other hand, when a chromium compound thin film is formed as the opaque film, or a compound thin film such as MoSiN, MoSiON, SiON, SiN is formed as a semi-transmission film (phase shifter film), the film is usually formed by the reactive sputtering method such as the DC magnetron sputtering. However, during the film formation, the compound is also deposited on the surface of a target, and electric discharge becomes unstable (as a result, particles are generated by abnormal discharge). Therefore, there is a problem that a defect is liable to occur in the photo mask blank. Furthermore, the reactive sputtering method has a lower deposition rate and therefore has a problem of a bad productivity, as compared with the usual non-reactive DC magnetron sputtering method.
When the compound target is used to form the film by an RF magnetron sputtering method instead of the DC magnetron sputtering method, plasma during the film formation is widely spread as compared with the DC magnetron sputtering method. Therefore, the film is undesirably deposited inside a chamber, and acts as a generation source of particles on the mask blank and, as a result, there arises a problem that the defect is liable to occur in the photo mask blank.
Moreover, in consideration of precision of a size recently required for the mask pattern, it has been necessary to thin a resist and opaque film during pattern formation. However, in a thin film forming method that uses the conventional DC magnetron sputtering method, the chromium film is inferior to a bulk film in density and denseness. As a result, a sufficient optical density cannot be obtained, and a demand for thin film formation cannot be satisfied.
The present invention has been developed to solve the aforementioned problems, and a first object thereof is to reduce a warp of a substrate by a film stress generated in a photo mask blank (relax and control the film stress).
Moreover, a second object of the present invention is to thin a film by enhancement of density and denseness, particularly to thin an opaque film by enhancement of a shielding property, and to enhance resistance to chemicals and resistance to light by enhancement of denseness.
Furthermore, a third object of the present invention is to reduce film defects by reduction of particles by abnormal discharge in a reactive DC sputtering method or by reduction of the particles in a reactive RF sputtering method during formation of a compound opaque film or a compound semi-transmission film by a reactive sputtering method, and to enhance a deposition rate (enhance productivity) by acceleration of reactivity (promotion of reactivity).
Additionally, a fourth object of the present invention is to provide a high-quality photo mask blank and photo mask prepared in consideration of the aforementioned objects.
To achieve the aforementioned objects, the present invention has the following constitutions.
(Constitution 1) A method of manufacturing a photo mask blank for forming an opaque film or a semi-transmission film on a transparent substrate, the method comprising a step of forming the opaque film or the semi-transmission film onto the substrate by irradiating the substrate with an ion generated by an ion generator separately disposed in a film formation chamber during the deposition of the opaque film or the semi-transmission film on the transparent substrate by a sputtering method.
(Constitution 2) The method of manufacturing the photo mask blank according to Constitution 1, wherein the step comprises controlling a film stress of the opaque film formed on the substrate; defining (a warp amount of the substrate after film formation)xe2x88x92(a warp amount of the substrate before the film formation)=(a warp amount of the substrate generated by the film formation); and suppressing the warp amount of the substrate generated by the film formation to xc2x10.1 xcexcm or less.
(Constitution 3) The method of manufacturing the photo mask blank according to Constitution 1 or 2, wherein the step comprises directly introducing an inert gas into the ion generator from the outside of the film formation chamber; and ionizing the inert gas by the ion generator and irradiating the substrate with the ion.
(Constitution 4) The method of manufacturing the photo mask blank according to Constitution 1 or 2, wherein the step comprises directly introducing a reactive gas into the ion generator from the outside of the film formation chamber; and ionizing the reactive gas by the ion generator and irradiating the substrate with the ion.
(Constitution 5) A photo mask blank is prepared by the method according to any one of Constitutions 1 to 4.
(Constitution 6) A photo mask is prepared by using the photo mask blank according to Constitution 5.
According to Constitution 1, the opaque film or the semi-transmission film is formed onto the substrate by the sputtering method, and the substrate is irradiated with the ion generated by the ion generator (hereinafter referred to an ion source) separately disposed in the film formation chamber (a film material being deposited on the substrate is irradiated), so that density and denseness of a thin film can be enhanced. Thereby, the opaque film can obtain an effect that the opaque film can be thinned by enhancing a shielding property by the enhancement of density and denseness and that chemical durability can be enhanced by the enhancement of denseness. Moreover, the semi-transmission film (phase shifter film) can obtain an effect that the semi-transmission film is thinned by the enhancement of density and denseness, and the chemical durability, irradiation durability, and the like are enhanced by the enhancement of denseness. In this case, when an irradiation energy of the ion emitted from the ion source is raised, the density and denseness can be enhanced.
Moreover, according to Constitution 1, since the substrate is directly irradiated with the ion from the ion source during sputtering deposition, it is possible to control a film stress. Thereby, for the opaque film, it is possible to relax or control the stress of the opaque film. Concretely, for example, a Cr film formed by sputtering without ion irradiation has a tensile stress. However, according to the present invention, the substrate is directly irradiated with the ion from the ion source during the sputtering deposition, and the irradiation energy is controlled, so that the tensile stress can be reduced, also be controlled to be zero, or further be controlled to be on a compressive stress side. Moreover, for the semi-transmission film (phase shifter film), it is possible to control the stress of the semi-transmission film.
When heat treatment is not performed as described later, the irradiation energy is preferably controlled in consideration of the reduction effect of stress and the enhancement effect of density.
Furthermore, according to Constitution 1, in a film formation process of the compound opaque film or the compound semi-transmission film by the reactive sputtering method, the substrate is directly irradiated with the ion from the ion source during the sputtering deposition. Thereby, reaction is accelerated (promoted) in the vicinity of the substrate and efficiently carried out. Therefore, deposition rate can be raised and productivity can be enhanced as compared with a conventional reactive sputtering method in which the substrate is not irradiated with the ion from the ion source.
In the present invention, a preferable type of the ion source may irradiate ions of a high current density and low energy so as to establish a purpose of improvement of a film quality, and, specifically, may be, for example, an RF type, end hall type, Kaufmann type, and ECR type, but this invention is not limited to the above-mentioned types of ion sources.
According to Constitution 2, the method of Constitution 1 is used to control the stress of the opaque film formed on the substrate, and it is possible to suppress the warp amount of the substrate generated by the film formation to xc2x10.1 xcexcm or less, assuming that (the warp amount of the substrate after the film formation)xe2x88x92(the warp amount of the substrate before the film formation)=(the warp amount of the substrate generated by the film formation).
In Constitution 2, the method of Constitution 1 is used to control the stress of the opaque film or the semi-transmission film formed on the substrate. Furthermore, the stress of the opaque film or the semi-transmission film is controlled by applying thermal treatment or laser irradiation treatment. Thereby, it is possible to suppress a change amount or a variable from a warp state measured before the film formation to xc2x10.1 xcexcm or less, assuming that (the warp amount of the substrate after the thermal treatment or the laser irradiation treatment)xe2x88x92(the warp amount of the substrate before the film formation)=(the change amount from the warp state measured before the film formation).
Concretely, for example, when the irradiation energy of the ion source is changed, the stress of the opaque film is controlled to be on the compressive stress side. When the film is subjected to the thermal treatment or the laser irradiation treatment, the stress of the opaque film can be reduced and controlled to be in the vicinity of zero. Additionally, the ion irradiation energy can be controlled by a beam acceleration voltage and anode current. Moreover, for example, when the stress of the semi-transmission film is a compressive stress, the film is subjected to the thermal treatment or the laser irradiation treatment, and the stress of the semi-transmission film can be reduced or controlled to be in the vicinity of zero. In this case, it is unnecessary to control the irradiation energy of the ion source with a good balance with the stress reduction effect as described above. It is possible to aim only at the enhancement of the density, when the irradiation energy of the ion source is controlled. Therefore, the density can further be enhanced.
Additionally, a thermal treatment temperature is preferably 150xc2x0 C. or more, 200xc2x0 C. or more, 250xc2x0 C. or more, 300xc2x0 C. or more, 350xc2x0 C. or more, 380xc2x0 C. or more, or 550xc2x0 C. or more. In this case, when the thermal treatment temperature is higher, an internal stress can be reduced, but a change amount of transmittance also increases. Additionally, when the temperature is excessively raised, a time of temperature rise or drop is lengthened. This causes a problem of deteriorated productivity. Therefore, the thermal treatment temperature is preferably 700xc2x0 C. or less. A thermal treatment time may be, for example, one minute or more as long as heat is conducted through the entire semi-transmission film within this time.
An atmosphere for the thermal treatment preferably includes no reactive atmosphere such as oxygen. If the reactive atmosphere is included, a composition of a film thickness direction is changed by the thermal treatment. Therefore, a preferable atmosphere includes inert gases such as nitrogen and argon.
Additionally, the thermal treatment may be performed after the semi-transmission film is formed on the transparent substrate (in a blank state) or after the semi-transmission film is patterned (in a mask state). Additionally, when a fine pattern is thermally treated at a high temperature, a pattern shape is possibly deteriorated. Moreover, the thermal treatment performed in the blank state has an effect that a film quality fluctuation in the subsequent baking process of the resist (200xc2x0 C. or less, e.g., about 180xc2x0 C.) is suppressed. In order to obtain the effect, the film is preferably thermally treated at a temperature which is higher than the baking temperature of the resist (e.g., 200xc2x0 C. or more).
According to Constitution 3, the inert gas is directly introduced into the ion generator from the outside of the film formation chamber and ionized by the ion generator, and the substrate is irradiated with the ion. Thereby, the inert gas ion can efficiently be supplied to the substrate as compared with introduction of the inert gas only via a sputtering gas introducing port. Therefore, the aforementioned reduction effect of the film stress and the enhancement effect of the film density can further be raised.
According to Constitution 4, the reactive gas is directly introduced into the ion generator from the outside of the film formation chamber and ionized by the ion generator, and the substrate is irradiated with the ion. Thereby, the reactive gas ion can efficiently be supplied to the substrate as compared with the introduction of the reactive gas only via the sputtering gas introducing port. Therefore, a reaction speed can further be enhanced, the aforementioned reduction effect of the film stress and the enhancement effect of the film density can further be raised, and controllability of the film is also satisfactory. Moreover, when the reactive gas is introduced only via a gas introducing port for the ion source, an amount of the reactive gas to be introduced into the film formation chamber can be reduced as compared with the introduction of the reactive gas only via the sputtering gas introducing port. As a result, since generation of the compound on the target can be inhibited, abnormal discharge in the reactive DC sputtering method can be reduced. Moreover, the film is inhibited from being deposited inside the chamber, the particles in the reactive RF sputtering method can be reduced, and this can reduce the film defects.
According to Constitutions 5, 6, there can be provided a high-quality photo mask blank and photo mask prepared in consideration of various factors. Such factors may be, for example, the reduction of warp of the substrate, thinning of the film by the enhancement of density and denseness, enhancement of chemical durability and irradiation durability by the enhancement of denseness, reduction of film defects during preparation of the compound opaque film or the compound semi-transmission film by the reactive sputtering method, and the like.